Enda King discusses the latest SSC research on ACL Injuries with IMeasureU’s Dan Savin.

Dr Enda King, Head of Performace at SSC Sports Medicine discusses the latest SSC research on Anterior Cruciate Ligament (ACL) Injuries with Dan Savin on IMeasureU’s Research Review.

About Enda King

In early 2019 Enda completed his PhD through the University of Roehampton in London exploring the influence of 3D Biomechanical analysis on outcomes after ACL reconstruction.

His greatest areas of expertise lie within hip and groin related, as well as knee / ACL rehabilitation, and he is committed to performing innovative research to develop robust methods for injury prevention and rehabilitation in elite sport.

Enda has over 20 peer-reviewed publications and regularly travels to speak at international conferences on groin injuries, ACL Return To Play and Return To Performance After Injury. Enda also authored the hip and groin chapter in “Sports Injury Prevention and Rehabilitation”. Enda in his presentation will explore the role of 3D biomechanical analysis in RTP after ACL Reconstruction.

For further information on ACL Surgery or to make an appointment with an SSC Clinician specialising in ACL Repair please contact info@sportssurgeryclinic.com
Interview with Enda King


It would be great if you could tell us a little bit more about who you are, what you do at SSC, and your journey to your role?

I have been at the UPMC Sports Surgery Clinic for over 10 years now. My current role is as head of performance. I am a Physiotherapist by trade. I have done my undergrad here in Trinity College in Dublin, and I have spent some time studying in Curtin University for my masters in Perth and have finished a couple of years ago with my PhD in 3D Biomechanics and ACL reconstruction in University Roehampton in London. I have picked up various strength and conditioning qualifications along the way through the UKSCA and the NSCA over in the states. My current role is probably three pronged: Number one is that I am involved in Business Development and Service Provision in the Sports Medicine Department in UPMC Sports Surgery Clinic. My main clinical roles are around residential rehab, so elite athletes and sub elite athletes come for biomechanical analysis and review, plus or minus intensive rehabilitation blocks. Off the back of that here with us in Dublin, I am involved in the academic research, principally around ACL and groin, but mostly around the use of 3D biomechanics in lower limb injuries in particular. So it’s a nice varied case now and it keeps everything interesting. It makes the weeks fly by.

I know you’re a busy guy and you’ve got a lot on your plate. I actually wanted to dive in in a bit more detail to your most recent publication. So I think it was back in February you published your two year follow up study, looking at the factors influencing returning to play and re rupture in class 1 elite athletes. So could you tell us a bit more about how that study came about and what the objectives of the research were?

I suppose one of the benefits of working in a place like the UPMC Sports Surgery Clinic is you get large volumes of the same kind of athlete/patient. We are very lucky to have a number of very experienced, talented and prolific knee surgeons in the clinic led primarily by Mr. Ray Moran our Director of Medicine, who would have a very substantial practice himself who would do about 600/700 ACL reconstructions per year, along with his colleagues Mark Jackson and Cathal Moran as well. We have this large cohort of a clinic that we are working through all the time and one of our expansion service wise was to enhance the physical assessment and follow up of these athletes post-surgery. These guys are doing a huge numbers of surgeries, but the outcomes physically can be a little inconsistent because of individuals of that athlete’s application but also they are going off to be rehabbed in different countries in the world. We wanted to try and offer some continuity, care and some systematic analysis to benchmark these athletes through. Our Director of Sports Medicine Andy Franklin Miller set up a biomechanics lab here in the clinic. We have two of them running concurrently and we set up a pathway to look at reviewing these athletes pre-op and at 3, 6 and 9 months after, and then obviously looking at the follow up after 2 years and we are currently most of our way through our 5 year follow up in this cohort as well. The idea being is that number one, we see lots of them, we think they do well- but do they do well? Number two is who or how many have issues and what are those issues. Number three is trying to rate that back from a biomechanical analysis point of view- can we identify through testing or through your demographic data or surgical data- who has a better chance of doing well or poorly, and can we intervene more proactively, because the majority of these athletes do quite well. There is a lot of scare mongering around ACL and outcomes and who gets back and re-rupture rates- clinically that didn’t necessarily follow up with what we were seeing, but unless you were tracking them all, we have 90/95% follow up in this cohort, unless you are tracking them and seeing what does happen, it’s very hard to make substantial comment’s one way or another. It was built off I suppose a desire to see how these athletes are turning out. Those who are not turning out as desired, how many are there, why is it happening and then can we be more proactive and evolve our care pathway to try and cater for them as much as possible.

With such a large study I’m sure that getting all the athletes back in through your doors for 2 years is a real challenge. Did you have much drop off or were you pretty successful in terms of what you were able to do?

I think you have to begin with the end in mind- when you lay out the journey for the athletes and how having your surgeries is the first step in the ladder, the testing is the next step, return to play is the next step but that we are with you not just to get you in and out and get your surgery and away you go, we are with you to make sure that it works out to the best outcome. The majority are actually delighted to get the follow up and be involved and see how things are going and are very interested in giving feedback on the process and how they’re doing. We spent a lot of work on trying to have a defined care pathway that all of the athletes fed into. People naturally opt out or move different country, however it captures the vast majority of these rather than cherry picking some athletes here and there or geography pertaining to it. The biggest job was getting a defined path in your place, making sure all the surgeons were feeding into it, and then it becomes self-fulfilling in that you’re coming because we have quite calibre surgeons but also you are coming for the package; you are coming because you know you are going to be looked after afterwards- you are coming with an expectation to be tested because your team mate has been tested or your cousin has been tested or whatever else. It expands beyond the ‘I’m coming because I ruptured by ACL can you fix me?’ to ‘Can you leave me back to where I was pre-injury?’ which is partly structural and partly physical. People want to give their story, they want to be followed up. We’re very lucky I think we had 95% follow up over 2 years and we are currently trending at over 90% for 5 years, so like people are buying into the process.

I appreciate it was a large study with lots of participants. Could you just touch on what your main findings were?

If you are looking for outcomes in relation to ACL, they are commonly related to return to play, to second injury and pain or ongoing issues of patients reported outcomes. I think that one of the unique things in this cohort/registry is that the mass majority of all were returning to field sports, so when you are comparing cohorts, I mean one of the best ways of avoiding ACL injuries is don’t change direction or land, so if you are looking for second injury groups you need to be focusing and analysing those going back to the highest risk sports- otherwise it is like comparing apples and pears. We have a high return to play rate over 2 years of 81% with the vast majority of those who hadn’t returned were for psychosocial reasons such as they didn’t feel ready or work getting in the way- very few, if any at all, hadn’t returned due to knee function. We found that the re injury rate for Patellar Tendons was 1.3%- which would be relatively low compared to the comparative literature, and 8.7% for our hamstring tendons. There seems to be a bias towards a higher second re rupture rate of our hamstring tendons. The injury rate in the Contralateral knee was about 6.6%. So the interesting bit also in return to play was that there was no relationship between time to return to play and second injury- so whether you return from 6 to 9 months, 9 to 12 months, or 12 to 15 months, that didn’t influence your re injury rate. There is a lot of discussion around that you shouldn’t go back for 2 years or 1 year etc., but there are a lot of athletes that successfully return without second injury at the 6 month mark, so we know that there is a healing process that needs to take place. We have no measure of that healing process- there is no way of testing how strong the graft is or how mature the graft is. We know that process can go to the 2 year mark and we know know the vast majority of athletes return without issue before 2 years. The role then of physical function and your physical capacity on your return obviously will take a greater importance and that is where our future research has moved on to. The other part is from our Pre and Intraoperative data, it was very difficult to predict who would have a second injury. So if you were to sit down in the office in front of Ray Moran and you were a male, whatever age, sport etc. and he has your Intraoperative findings, it is very difficult based on only on that data to say well you are more likely to do well or you are not more likely to do well, so naturally like all these things it is more multifactorial than that. Some of our future work now is looking to bring the demographic and operative data in with the biomechanical data to see if we can create more robust algorithms around that as well. I think the take home messages were that is that ACL reconstruction is a successful way of returning to high demand sports, the re injury rates are low overall, lower for Patellar Tendons. What we have done which is most cared for within this is, obviously there is the surgical data and it’s influences and outcomes, but it is also the influence of a pathway. If you have a pathway that reviews athletes at regular time points and provides objective feedback; that is it positive in a return to play point of view as they are motivated and goal driven to return, and is it positive in a second injury/pain point of view because you are catching them early physically below some of the benchmarks you’re looking for. Million dollar question is how good is good enough, which obviously is very individual. It’s amazing how many athletes do a lot of rehab and don’t look much different physically between 3 months, 6 month and 9 month reviews, our process is around not so much what you do or the what the right/wrong exercises are, but physically how you look now and how you look in X number of weeks/months time, which brings a huge degree of objectivity- its great from a practitioner point of view because your work is under the microscope the whole time. Now we would only rehab a small proportion of these because Geographically they span across the country, but if you are rehabbing athletes and they are re tested after 6 months, 9 months and you assess 3 main goals and those measures are not trending very strongly in the right direction, naturally we all blame the athlete/patient because they never do what they tell us, but the reality is maybe we have to look back at our coaching, periodisation, the way we are programming our exercises. So it is a phenomenal feedback loop in terms of a) objectively benchmarking you against other athletes but also b) benchmarking my programming because what is working for that athlete may not be progressing at the same rate as would be expected for the effort that another athlete is putting in.

To be fair that brings me quite nicely onto my next question. Obviously we have seen a lot of athletes over a long period, and ultimately I guess the goal of any research is to inform practice and best practice at that. Have you used the results of this particular study or have you learned anything over the period of time that has caused you to change your practice?

In terms of this study I suppose it is potentially more pertinent to the surgeons, then to myself. I’m not going to select the graft type myself. Certainly I would wholeheartedly encourage Patellar Tendon grafts over hamstring grafts based on this information. A lot of the movement towards hamstring grafts and other grafts has been due to anterior knee pain. The primary reason you’re having your ACL reconstructed is to provide structure stability to the knee and not have a second injury. You want to pick whatever graft that does that first and foremost. Anterior knee pain is a rehab problem; certainly a Patellar Tendon graft may leave you more susceptible to anterior knee pain, the same way a hamstring graft may leave you more susceptible to hamstring injury- but that’s still a rehab problem, which means I need to go back and redevelop a programme and achieve the outcomes off the back of that. The second thing is I would put after the 6 month marker I would put more emphasis on your physical ability to return to play rather than time from surgery, as it doesn’t seem to be supported based on this data that time after six months leaves you at higher/lower risk. It is interesting how there is a larger percentage of people injuring the previously healthy knee than there is the operated knee- there are a number of studies that are in final review at the minute around the biomechanical factors related to re rupture or injury to the Contralateral knee and a lot of it is around the frontal plane and Valgus, which would have got a lot of the previous press/coverage in the literature. We are finding that a lot of it is to do with your performance during drop jumps and stiffness. Trying to set a high enough bar in relation to that is something we are putting a lot more focus on going forward.

I know you mentioned that this whole process is rolling over into a 5 year period and you just mentioned there that you got some papers in the process of publication. What other research can we expect from you and your team particularly over the coming months is there anything exciting that’s due to be published?

We have a PhD student who is looking at the influence of visual distraction and neuroplasticity during ACL rehabilitation compared to healthy athletes to see what role visual distraction has in our coordination and task execution, but also as a rehabilitation tool to influence our motor learning and our ability to bridge that gap quicker. We also have a number of papers looking at the biomechanics of female second injuries- so that the re ruptured data we have already outside of the registry, the biomechanical data has all been based on male athletes. We are also trying to use machine learning and AI to combine the biomechanical data with the demographic data and Intraoperative data to try and begin to profile people at various time points to say ‘your risk is higher/lower and these are the variables that are most relevant to you’. We naturally break an athlete down to your strength measures, power plyo measures, motor control during various tasks, all of which are inter related as well. Rather than just saying one test is good/bad, it’s when we look at a battery of tests to shed a greater light on things going forward. There is a lot of very interesting stuff from that point of view. There’s a lot of potential in terms of how we rehabilitate our athletes but also on how we advise our surgeons and referrers as to the current status of an ACL rehab and where things should go. People are always looking for the green light- however there are a lot of people who may be insufficiently rehabilitated or they’re poor movers and they don’t have a second injury due to not having enough exposure to the sport as they go back, maybe their genetics get in the way- it is multi factorial. But rather than saying when am I ready, the question is when am I fully rehabilitated? What does that look like? And can begin to say that when you go back to play that’s when you step on the journey. It is interesting how many athletes especially come back for re assessment every preseason saying they feel good, they’re moving well, they just want to just re calibrate and see what are their area’s they have to work on again. Again, there is no such thing as perfect because I don’t know what it looks like, but there is better and there is poorer and if we can place you somewhere on that spectrum, you can be much more targeted in what you are doing either from a performance or rehabilitation point of view as well.

Do you ever think we can get to a level where we can predict risk or chances of ACL injury through Machine Learning and all the things you have just mentioned there?

I suppose when you look back now at what we were doing from a medical and sports science point of view 50 years ago, it’s not even comparable to now. If you go forward 50 years they would probably be laughing at what we are doing right now, from a technology and practice point of view. You can’t get too proud of your current work/practices. I think only truly when all the factors can be brought into play, like genetic type, anatomy, biomechanics, surgical data etc., only when all of that is fitted into a model you will see more accurate predictions in relation to ACL. Our re rupture rates are very low which when you’re looking to predict, the easiest thing from a prediction point of view is saying that ‘you are not going to re rupture’ because 98% of the time we’re going to be correct, so it is difficult to develop models off datasets where you have only a small percentage ending up having desire and undesired factors. So that makes things a little bit more difficult than let’s say a hamstring injury, where you know that a third of patients are going to have a second injury potentially. But I think will evolve all the time- technology will evolve in terms of how we can measure and how accessible it is. But I don’t think we will ever be able to say your magic number is this or that because it’s the chaos of the sporting environment doesn’t fully take into account of what we can objectively measure. But I think we will get better at getting people physically back to where they need to be. It’s amazing because I do various workshops with physios and teams and there is always a couple of ACL’s within the group, and despite the fact that they are practitioners how many of them have ongoing persistent physical datasets, just related to the initial injury and post-surgery periods and they just never restored their physical function independent of their joint stability etc. So I think if we can objectify it more towards not can I predict whether you are going to re rupture or not, because that will probably always be a bit of a challenge, but can I profile you to say that you are physically back to where you should be or not or back to normal whatever that is. That is the next hurdle rather than you can return in 3/6/9 moths or things like that.

Well you guys are clearly doing a good job if you need some more data for unsuccessful surgeries you obviously need to do a lesser job of the rehab and surgeons need to drop a couple of pegs

Well it’s like everything else. There will always be re injuries and the surgeons here will always be very proactive on injury and ACL prevention. They are not going to do themselves out of business because as long as you are jumping around and changing directions there are going to be primary and secondary ACL’s, but I think we can do a much better job here and everywhere in being more defined in the physical side of things. There are hundreds and hundreds on ACL reconstruction, very well defined process, yet there is almost no agreement/clarity on what you should look like at the end. So I think that is probably the biggest gap in where we can go going forward is our outcomes are good but where is the room for improvement. It’s restoring physical function. Ironically pain post ACL or intermittent knee fusion when they return to play is a much bigger issue than re rupture and second injury is. It is completely unnecessary. I think that’s where opportunities are going forward.

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